Cobalt(III)-Catalyzed and DMSO-Involved Allylation of 1,3-Dicarbonyl Compounds with Alkenes

Cobalt(III)-catalyzed allylation of 1,3-dicarbonyl compounds has been reported with in situ generated allyl reagents from alkenes and dimethyl sulfoxide (DMSO). This novel protocol enables a high regio- and stereoselective access for a broad range of allyl 1,3-dicarbonyl compounds. In the transformation, DMSO plays the role of a C1 source, and it incorporates with alkenes to form the allyl reagent allylic methyl thioether. Moreover, a multiple-step pathway has been proposed to rationalize the mechanism study, which involves silver-mediated coupling, Co(III)-catalyzed π-allylation, and intermolecular nucleophilic substitution.

Bromine-Promoted One-Pot Furo[b]annulation and α-C(sp2)-Thiomethylation Cascade of (E)-3-Styrylquinoxalin-2(1H)-ones with Dimethyl Sulfoxide

A new process has been developed for the bromine-promoted sequential (sp²)C = (sp²)C bond functionalization of (E)-3-styrylquinoxalin-2(1H)-ones and furo[b]annulation via the 5-exo-cyclization in dimethyl sulfoxide (DMSO). The reaction represents a novel strategy for the synthesis of 2-aryl-3-(methylthio)furo[2,3-b]quinoxalines and involves 3-(1,2-dibromo-2-arylethyl)quinoxalin-2(1H)-ones and 2-arylfuro[2,3-b]quinoxalines as key intermediates. Furthermore, DMSO was converted to dimethyl sulfide in situ, which served as the methylthiolation reagent in the reaction. This protocol constitutes an efficient and convenient method for the annulation and methylthiolation of (E)-3-styrylquinoxalin-2(1H)-ones bearing a wide range of functional groups in high yields at room temperature.

Recent Advances of Green Catalytic System I2/DMSO in C–C and C–Heteroatom Bonds Formation

Developing a green, practical and efficient method for the formation of C–C and C–Heteroatom bonds is an important topic in modern organic synthetic chemistry. In recent years, the I2/DMSO catalytic system has attracted wide attention because of its green, high efficiency, atomic economy, low cost, mild reaction conditions and it is environment-friendly, which is more in line with the requirements of sustainable chemistry. Heteroatom-containing compounds have shown lots of important applications in pharmaceutical synthesis, agrochemicals, material chemistry and organic dyes. At present, the I2/DMSO catalytic system has been successfully applied to the synthesis of various heteroatom-containing compounds. The C–C and C–Heteroatom bonds have been formed efficiently, which has been proved to be a green and mild catalytic system. In this review, the research achievements of the I2/DMSO catalytic system in the formation of C–C and C–Heteroatom bonds from 2015 to date are described, and the research area is prospected. This review attempts to reveal the general law of iodine catalysis and lay a foundation for the design of new reactions.

Application of DMSO as a methylthiolating reagent in organic synthesis

In the past decades, DMSO has been widely used not only as a common solvent but also as an environmentally benign oxidant in various organic transformations. Most strikingly, DMSO can be used as a sulfur source to construct methylthiolated building blocks of potential biologically active molecules, which is a remarkable achievement in the field of organic sulfur chemistry. The purpose of this review article is to summarize and discuss the main developments in the application of DMSO as a methylthiolating reagent to introduce the -SMe functionality in organic synthesis.

Diverse 3-Methylthio-4-Substituted Maleimides through a Novel Rearrangement Reaction: Synthesis and Selective Cell Imaging

A transition metal-free protocol for the preparation of fluorescent and non-fluoresent 3-methylthio-4-arylmaleimides in a single step through a new rearrangement from thiazolidine-2,4-diones is described. By employing the optimized reaction conditions, a broad scope of derivatives was prepared in ≤97% yield. The reaction tolerated several substituted aryl groups, including the challenging preparation of pyridyl-containing derivatives. A series of control experiments strongly suggested that the new rearrangement involves a key isocyanate intermediate and a further reaction with in situ-generated methylthiomethyl acetate. The photophysical properties of some of the synthesized derivatives as well as their use in live cell imaging were also investigated, revealing that some of the substituted maleimides are capable of selectively staining different regions of the cells.

Selectfluor-Mediated Synthesis of β-Acyl Allyl Sulfones/β-Acyl Allyl Benzotriazoles from Ketones/Acetylenes, Aryl Sulfinates/Benzotriazole, and DMSO as a Dual-Carbon Synthon

A Selectfluor-mediated approach for the synthesis of β-acyl allyl sulfones/β-acyl allyl benzotriazoles with excellent atom economy from readily available acetophenones/aryl acetylenes, aryl sulfinates/benzotriazoles, and dimethyl sulfoxide (DMSO) is described. In this protocol, DMSO acts as a dual-carbon synthon, resulting in a transition-metal-free construction of two C-C and one C-S or two C-C and one C-N bonds in one pot. This approach is extended to generate chemically diverse compounds. Additionally, β-acyl allyl sulfones/β-acyl allyl benzotriazoles were prepared from acetylenes instead of acetophenones.

Regioselective direct sulfenylation of glycals using arylsulfonyl chlorides in the presence of triphenylphosphine: access to C2-thioaryl glycosides

Cheap and easily available arylsulfonyl chlorides as a sulfur source reductively couple with glycals in the presence of triphenylphosphine to afford C2-thioaryl glycosides.

Synthesis of Cyclopentenes and Cyclohexenes Via Cobalt(II)-Catalyzed Oxidative Cyclization

A unique method for the synthesis of cyclopentenes and cyclohexenes has been achieved by the coupling of diketones and alkenes under cobalt(II) catalysis and dimethyl sulfoxide involvement. Under optimal conditions, the formation of five- and six-membered rings can be readily controlled by the α-position substitution of styrenes. This process is proposed to proceed through a reaction sequence of oxidative coupling (mediated by K₂S₂O₈), regioselective alkene insertion (promoted by cobalt), and intramolecular attack of the resulting allylcobalt species on the carbonyl group or methyl group in the reactive methylene process.

Diversity-oriented synthesis of imidazo[1,2-a][1,3,5]triazine derivatives from 2-amine-[1,3,5]triazines with ketones

An I₂-mediated annulation of 2-amino[1,3,5]triazines and ketones for the synthesis of imidazo[1,2-a][1,3,5]triazines is presented. Electron rich, or electron poor acetophenone and heterocycle ketones, as well as propiophenone, are functionalized with 2-amino-[1,3,5]triazines. Another class of imidazo[1,2-a][1,3,5]triazines tethered with an additional 1,2-dicarbonyl motif through the combination of annulation and C-H functionalization were obtained instead by changing the reaction conditions. The new methods are practically straightforward and applicable on a gram scale.

Synthetic developments on the preparation of sulfides from thiol-free reagents

This critical review covers the main thiolating reagents with respect to their characteristics and reactivities. In fact, they are complementary to each other and bring different thiolation strategies, avoiding the hazardous thiol derivatives.

Recent Advances in Iodine-Promoted C-S/N-S Bonds Formation

Sulfur-containing scaffold, as a ubiquitous structural motif, has been frequently used in natural products, bioactive chemicals and pharmaceuticals, particularly C-S/N-S bonds are indispensable in many biological important compounds and pharmaceuticals. Development of mild and general methods for C-S/N-S bonds formation has great significance in modern research. Iodine and its derivatives have been recognized as inexpensive, environmentally benign and easy-handled catalysts or reagents to promote the construction of C-S/N-S bonds under mild reaction conditions, with good regioselectivities and broad substrate scope. Especially based on this, several new strategies, such as oxidation relay strategy, have been greatly developed and accelerated the advancement of this field. This review focuses on recent advances in iodine and its derivatives promoted hybridized C-S/N-S bonds formation. The features and mechanisms of corresponding reactions are summarized and the results of some cases are compared with those of previous reports. In addition, the future of this domain is discussed.

NBS-activated cross-dehydrogenative esterification of carboxylic acids with DMSO

A convenient and versatile cross-dehydrogenative esterification of carboxylic acids with DMSO for preparing (methylsulfinyl)methyl esters has been developed in the presence of N-bromosuccinimide.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Transition metal-free α-methylation of 1,8-naphthyridine derivatives using DMSO as methylation reagent

A practical approach to the direct α-methylation of 1,8-naphthyridines under mild reaction conditions has been developed using simple and readily available DMSO as a convenient and environmentally friendly carbon source. This method is transition metal-free and highly chemoselective, shows good functional group tolerance, and uses DMSO as a methyl source, providing efficient and rapid access to an important compound class, 2-methyl-1,8-naphthyridines.

Iodine-Promoted Domino Oxidative Cyclization for the One-Pot Synthesis of Novel Fused Four-Ring Quinoxaline Fluorophores by sp3 C-H Functionalization

A method for the synthesis of novel fused four-ring quinoxaline skeleton has been described by an I₂ promoted sp³ C-H functionalization between 1,2,3,3-tetramethyl-3H-indolium iodides and 1,2-diamines. This transformation proceeds smoothly under metal- and peroxide-free conditions through a sequential iodination, oxidation, annulation and rearrangement. Moreover, 8,9-dichloro-5,12,12-trimethyl-2-(trifluoromethyl)-5,12-dihydroquinolino[2,3-b]quinoxaline showed good photophysical properties and was used in live cell imaging, indicating the potential value of this skeleton as a fluorophore in probes.

I2-Promoted Multicomponent Dicyclization and Ring-Opening Sequences: Direct Synthesis of Benzo[e][1,4]diazepin-3-ones via Dual C-O Bond Cleavage

A novel and efficient formal [4 + 2+1] annulation of aryl methyl ketones and 2-aminobenzyl alcohols for the synthesis of benzo[e][1,4]diazepin-3-ones is reported. This reaction successfully affords diverse seven-membered ring lactams via dual C-O bond cleavage. A preliminary mechanistic study showed that a multicomponent dicyclization and ring-opening sequence might occur, with the introduction of methyl sulfide proposed as the last step. This efficient strategy with mild reaction conditions and a broad substrate scope has potential applications in chemistry and medicine.

Cobalt-Catalyzed Allylation of Amides with Styrenes Using DMSO as Both the Solvent and the α-Methylene Source

An efficient synthesis of privileged allylic amines has been developed via cobalt-catalyzed allylation of amides with styrenes, in which DMSO was used as both the solvent and the α-methylene source. This transformation features high yields, and selectivity for the (E)-isomer of the linear product. Through the experimental and computational investigations, a sequential K₂S₂O₈-mediated oxidative coupling/cobalt-assisted regioselective alkene insertion/β-H elimination/alkene dissociation/hydride transfer process has also been deduced.

Employing thiocyanate salts as a nitrogen source via CN bond cleavage: divergent synthesis of α-ketoamides and 2-acyloxazoles

A switchable procedure for the synthesis of α-ketoamides and 2-acyloxazoles from aryl methyl ketones and thiocyanate salts is reported.

I2/DMSO-mediated multicomponent reaction of o-hydroxyaryl methyl ketones, rongalite, and DMSO: access to C3-sulfenylated chromones

An efficient I₂–DMSO reagent system-mediated multicomponent reaction strategy for the synthesis of C3-sulfenylated chromones from o-hydroxyaryl methyl ketones, rongalite, and dimethyl sulfoxide has been developed.

Metal-Free Oxidative Thioesterification of Methyl Ketones with Thiols/Disulfides for the Synthesis of α-Ketothioesters

A direct C_sp3-H bond oxidative thioesterification of methyl ketones with aromatic thiols/disulfides promoted by TBAI/K₂S₂O₈ has been developed. The reaction provides successfully a simple and efficient method for the synthesis of functionalized α-ketothioesters of aromatic thiols. This practical methodology exhibits readily available starting materials, large-scale applicability, synthetic application, and broad functional group tolerance. A possible mechanism for the transformation is proposed.

Cesium carbonate-promoted synthesis of aryl methyl sulfides using S-methylisothiourea sulfate under transition-metal-free conditions

In the presence of cesium carbonate, an efficient synthesis of aryl methyl sulfides by the reactions of aryl halides with commercially available S-methylisothiourea sulfate is developed. This odourless and highly crystalline solid can be used as the substitute for malodorous methanethiol. The gram-scale reaction also proceeds smoothly without the use of column chromatography separation. Similarly, 2-(dimethylamino)ethylthio and cyclopropylmethylthio groups can be easily introduced into the aromatic rings from the corresponding S-[2-(dimethylamino)ethyl]isothiourea dihydrochloride and S-cyclopropylmethylisothiourea hydrobromide. The possible reaction mechanism is proposed. It is believed that this route to aryl alkyl sulfides is well competitive with currently known methods due to its wide substrate scope, excellent yields, easy operation and transition-metal-free conditions.

Selective access to dipyrazolo-fused pyridines via formal [3 + 2 + 1] heteroannulation of methyl ketones with pyrazol-5-amines

A fascinating new form of the Hantzsch reaction with methyl ketones and pyrazol-5-amines for the selective synthesis of dipyrazolo-fused pyridines has been discovered.

Iodine-catalyzed synthesis of N,N′-diaryl-o-phenylenediamines from cyclohexanones and anilines using DMSO and O2 as oxidants

An I₂/DMSO system has been successfully applied to synthesize N,N′-diaryl-o-phenylenediamines from cyclohexanones for the first time.

Iodine/DMSO oxidations: a contemporary paradigm in C–N bond chemistry

A new era in the organic synthetic world is demanding greener protocols for the execution of reactions.